1. Field
The present disclosure relates to a wireless communication, more specifically a method and apparatus of periodic channel state information reporting applicable to a system supporting TDD (Time Division Duplex)-FDD (Frequency Division Duplex) joint operation.
2. Discussion of the Background
A wireless communication system may support Frequency Division Duplex (FDD) scheme and Time Division Duplex (TDD) scheme. In the FDD scheme, an uplink transmission and a downlink transmission may be simultaneously performed in a cell because a carrier frequency for an uplink (UL) transmission is different from a carrier frequency for a downlink (DL) transmission exists. In the TDD scheme, with respect to one cell, an uplink transmission and a downlink transmission are distinguished from each other based on different time slots. In the TDD scheme, a base station and a user equipment perform switching operations between a transmission mode and a reception mode because the same carrier is used for both an uplink transmission and a downlink transmission. In the TDD scheme, a Special Subframe may be added to provide a guard time for switching between the transmission mode and the reception mode. The Special Subframe may include Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot (UpPTS). According to the TDD scheme, resource amounts for the uplink transmission and resource amounts for the downlink transmission may be asymmetrically assigned through various uplink (UL)-downlink (DL) configurations.
Currently, remaining frequency resources are scarce and various technologies have been utilized in wide frequency bands because of the frequency resource scarcity. For this reason, in order to provide a wideband bandwidth for supporting higher data-rate requirements, each of scattered bands has been configured to satisfy basic requirements to operate an independent system and a carrier aggregation (CA) scheme, which aggregates various frequency bands into one system, has been adopted. Here, each frequency band or carrier capable of an independent operation may be defined as a component carrier (CC).
Further, a wireless communication system uses a link adaptation in order to make the maximum use of a given channel capacity, to control Modulation and Coding Scheme (MCS) and Transmission Power according to a given channel. Here the link adaptation means changing modulation and channel coding scheme depending on a wireless link condition to optimize the communication performance. To perform this link adaptation at a base station, the periodic feedback of channel status information by a terminal is required, and the terminal carries out the periodic channel status reporting for it.
Recently, considered is a TDD-FDD joint operation technique supporting the CA of an FDD band (or carrier) and a TDD band (or carrier) and/or a dual connectivity thereof. A terminal supporting TDD-FDD joint operation may be configured with a TDD serving cell and an FDD serving cell simultaneously. However, the existing periodic channel status reporting method assumes only the periodic channel status reporting in case that a terminal is configured with a single serving cell, or the terminal is configured with an FDD or a TDD type serving cell; it does not consider the case that a TDD serving cell and an FDD serving cell are configured at the terminal. Therefore, there exists a need for a method of a periodic channel status reporting for a terminal configured with TDD-FDD joint operation.